Pipes used to carry liquids and gases commonly transport all types of materials including water, natural gas and liquid sewage. Over time, these pipes require servicing and cleaning. MacNeil et al. disclose an automated process for cleaning or restoring the inside of a pipe in U.S. Pat. No. 6,206,016. As yet, however, nobody has disclosed a device with an automated process for cleaning or restoring the inside of a pipe that can remain in the interior of the pipe, even under active flow conditions.
The interior surface of a pipeline carrying solids, liquids and gases generally degrades over time as the pipe walls interact chemically and physically with the substances flowing through them and air. In particular, a sewer system's interior walls corrode and deteriorate because corrosive materials contaminate the surface, degrading the metal and concrete used to build the sewer pipe. The corrosive material arises from both the sewage and waste water itself, and also from the digestible by-products of bacteria found in the sewage which proliferate in the anaerobic environment. The corrosion causes the walls of the sewer pipe to physically decay, eventually reducing their overall thickness.
The principle source of corrosion is sulfuric acid, which arises as a product of the reaction of sewer gases with water and air in the sewer pipe and the sewer environment itself. Various metal sulfates found in the sewage quickly convert into hydrogen sulfide by reducing to sulfide ions in the waste water, combining with hydrogen in water and outgassing above the liquid as hydrogen sulfide gas. Additional hydrogen sulfide originates from bacteria-containing contaminants which accumulate on the relatively rough concrete below the maximum liquid level. Bacteria found in these accumulations thrive in the anaerobic sewer environment producing hydrogen sulfide gas as a respiratory by-product. Oxygen from the liquid below and oxygen condensing from the water in the air react with the hydrogen sulfide on the pipeline walls creating the highly corrosive sulfuric acid. The sulfuric acid attacks the calcium hydroxide in the concrete sewer walls leaving calcium sulfates which ultimately crumble and fall off the interior of the wall substantially reducing its thickness.
The waste water level varies over the course of a 24-hour period. The flow is at its lowest level between 1:00 a.m. and 6:00 a.m. in the morning but it rises distinctly in the daytime when the pipe may operate near capacity. Because of the gaseous nature of the hydrogen sulfide, the pipe walls are predominately corroded in the portions of the wall above the minimum liquid level. Portions of the walls which are always below the water level are not subjected to such high concentrations of hydrogen sulfide gas or sulfuric acid and consequently do not experience the same level of decay.
Eventually the sewer walls must be restored or they can suffer permanent damage leading to great expense. The restoration process is a two-step operation that consists of first scarifying the interior pipe surface to remove the contaminants (including any possibly existing outer layers of corrupted concrete) from the surface of the pipe, i.e. a process herein defined as scarifying, and then applying a protective coating over the newly cleaned (scarified) pipe surface. Attempting to apply a protective coating without first scarifying the pipe surface is futile because it does not stop the decay that has already begun underneath the coating. Furthermore, the protective coating itself does not adhere well to the contaminated surface. Thus, scarifying is an essential element of the restoration process.
As previously mentioned, the sewer typically operates at high capacity during the day with a decreased flow overnight. In order to restore the sewer pipes without diverting the flow (a costly and sometimes impossible alternative), a bulk of the work must be done at night during the brief period when the flow is at a minimum. As previously outlined, the restoration process involves both scarifying the pipe surface and applying a protective coat. In practice, the rate of restoration is impaired because manual scarifying takes a proportionally greater amount of time than does the application of the protective coat. Automated scarifying processes exist, e.g. MacNeil et al above, however, presently devices require insertion into the sewer assembly and then removal from the sewer, all during the brief period when the sewer flow is at a minimum. Consequently, a need exists for an automated scarifying or restoration apparatus that can remain in the sewer during the period when the waste water level is not at a minimum.